With just days to go before the Lords vote on whether to allow Rupert Murdoch to buy Channel Five, the media mogul's ambitions to expand his television interests have been plunged into uncertainty after the Australian government failed to secure parliamentary backing for its ambitious media ownership reforms.

In an almost exact mirroring of the communications bill currently going through parliament in the UK, the Australian government wants to scrap restrictions that prevent Mr Murdoch - who already has newspaper and pay television interests in Australia - from adding a terrestrial TV network to his media stable.

The government, which needs to secure votes from four independent Senators to secure a majority, is pushing to get the bill approved before parliament closes for its summer break at the end of this week.

But there is now little chance of the government getting the go-ahead for its plans to relax the country's media ownership laws when the debate resumes later today, after key independent senators yesterday objected to the plan.

"They're still thrashing out the details of a number of amendments there. I'm not sure if we're going to get a vote today," a spokesman for communications minister Richard Alston told Reuters. "It's pretty much a balancing act."

Mr Murdoch and Australia's richest man, media baron Kerry Packer, have fiercely lobbied for a more relaxed regime over the past few years, arguing that current laws have thwarted their growth options in Australia.

Under current rules, a television licence holder cannot own more than 15% of a newspaper in a capital city and non-Australian companies cannot own more than 15% of a TV station or 25% of a major newspaper.

Key independent senators in the upper house yesterday objected to the long-awaited proposal, revived over a year ago after heavy lobbying by the government to win the support of the opposition parties that hold a majority in the Senate.

They expressed concern that lifting restrictions on media ownership, which prevent proprietors from owning more than one TV station, newspaper or radio station in the same market, would threaten media diversity and compromise editorial content. One senator warned that an agreement is unlikely to be reached in the near term, despite the government's efforts to gain support for the bill this week. Trenchant opponents to the legislation, such as Senator Brian Harradine, want a key amendment introduced banning proprietors such as Mr Murdoch from owning a TV station and newspaper in the same city.

The government is almost certain to reject this, plunging the fate of the bill into doubt.

If it can secure the votes it needs to quickly push its bill through the upper house, Australia's media landscape will be radically remodelled with the new laws triggering a surge in corporate activity.

Despite the fierce debate surrounding cross-media ownership changes, there has been little opposition to scrapping foreign ownership limits. This would allow investors such as Sir Anthony O'Reilly's Independent News & Media to expand their Australian media portfolios. Other companies, including Pearson, are widely tipped to be on the prowl for cheap publishing assets if the rules are relaxed.

The Murdoch family's News Corporation controls over 50% of newspapers in Australia and has made no secret of its desire to snap up a television network.

The latest setback comes as the media mogul prepares to take advantage of recent changes in the US after regulatory authorities backed the removal of bans on ownership of newspapers, television and radio stations in the same market. He is expected to expand his Fox TV Network while retaining ownership of the New York Post.

The UK government is facing a similar setback to its communications bill with a hardcore of well-informed Labour peers, including the film producer Lord Puttnam, taking it to task over plans to relax media ownership laws

Lord Puttnam's proposal to insert a new public interest test into the communications bill that would make it harder for Murdoch and other newspaper proprietors to buy Five has now gained so much support that the government is now working to draft an amendment that would be acceptable to both sides.

While not getting rid of the clause completely, this would put another major hurdle in place if Murdoch decided to go after Five.

The House of Lords resumes its debate on the communications bill tomorrow and is expected to discuss the so-called "Murdoch clause" next Tuesday.